Electronic document scanners and facsimile machines transform an optical image of a document into an electric signal suitable for storing, displaying, printing or electronic transmission. These devices typically use illumination and optical systems to illuminate the object and focus a small area of the illuminated object, usually referred to as the “scan line”, onto an optical photo sensor array. This direction is typically called the scan width or X-direction. The entire object is then scanned by sweeping the illuminated scan line across the entire object, either by moving the object with respect to the illumination and optical assemblies, or by moving the illumination and optical assemblies relative to the object. This is typically called the scan length or Y-direction.
An optical scanner has a native or optical resolution that is the maximum sample rate of the object to be scanned. In a typical scanner this resolution is usually 600 or 1200 samples or pixels per inch (ppi). Typically a scanner can scan at a range of resolutions or sample rates ranging from a small fraction ( 1/20) of the optical resolution up to 2 times the optical resolution. For example a scanner with an optical resolution of 600 ppi could scan using a resolution ranging from 30 ppi up to 1200 ppi.
Images that scanners scan range in size from small objects or photos up to scans of full pages. Typically scanners allow the size of the scanned area or window to be adjusted to match the size of the object to be scanned. A typical scanner allows the window to be adjusted in the x and y directions from one pixel in length up to the full size of the scanning bed. Many scanners allow the user to select or adjust the scan area by doing a low-resolution scan and displaying the results on a computer monitor. The user can then use the mouse to select the scan area for the final scan. Once the final scan area has been selected, a final high-resolution scan is done and saved in computer memory or on the hard disk. The low-resolution scan may be referred to as a preview scan.
The illumination system in most scanners contains a lamp. The type of lamp for many scanners is a fluorescent bulb. Fluorescent bulbs are well suited for scanners in a number of ways: they are relatively energy efficient, they have a wide variety of phosphors available to allow proper color balance, and they have relatively long life. Fluorescent bulbs do have some disadvantages. One disadvantage is the time it takes a fluorescent bulb to warm up and produce a relatively constant light profile along the length of the bulb. Scanners solve this problem in a number of ways. Some scanners never turn the lamp off. This allows quick scan starts but reduces the useful life of the scanner and wastes energy. Other scanners turn the light on just before a scan and then wait until the bulb has stabilized before beginning the scan. This method uses less energy but the user must wait longer for the scan to start. Some scanners just turn the light on and scan before the light has stabilized. This allows a quick scan start but typically results in intensity variations over the scan area resulting in a poor quality scan.
There is a need for a scanning solution that starts the first scan quickly and retains high quality for the final scan.